There is a high demand for chemical sensor devices for detecting low concentration levels of analytes present in the liquid and gaseous phase. Specificity to particular analytes is also generally desired.
Chemical sensor devices often involve luminescent materials because luminescence lifetimes and intensities can be sensitive to the presence of external species or analytes. Fluorescent polymeric materials are particularly advantageous for sensor devices because the resulting fluorescence and other physical properties can be optimized and/or tailored for particular analytes through chemical structure changes of the polymer.
Charge conducting polymers are usually fluorescent polymers. Such polymers are capable of delocalizing charge throughout a substantial portion of the polymer by π-conjugation. The π-conjugated portion comprises a set of orbitals that can function as a valence band. The polymers can be doped with species that either donate or accept electron density, and an energy difference between the valence band and conduction band is referred to as a band gap. Moreover, other energy levels may be available in the band-gap or in higher energy levels having antibonding character.
Because charge delocalization results in the formation of various high lying energy levels, a variety of excited state structures are available upon absorption of energy by the conducting polymer. The luminescence yields of these excited state structures depend highly on polymer structure. The luminescence can be quenched by the presence of species capable of absorbing the energy contained by the polymer, resulting in the polymer returning to a ground state. The species can be an external species or internally located within the polymer, such as a side-group. One example of such quenching by internal species is through a π-stacking mechanism. Atoms involved in the π-conjugation can be positioned on top of other groups having geometrically accessible π-orbitals, forming a pathway for energy transfer.
Luminescent polymers are disclosed in U.S. Pat. No. 5,414,069 which describes an electroluminescent polymer having a main chain and a plurality of side chains. The main chain contains methylene or oxide groups and the side chains contain the electroluminescent groups such that the electroluminescent groups are not conjugated with one another. One method of modulating electroluminescent properties is by varying the spacing between the electroluminescent groups.
U.S. Pat. No. 5,597,890 relates to π-conjugated polymers that form exciplexes with electron donor or acceptor components. The polymer has a main chain of unsaturated units such as carbon-carbon double and triple bonds and aromatic groups. The side chains include single ring aryl groups.
Thus there remains a need to design polymers having maximal luminescent lifetimes for use in sensory devices, in particular where the luminescent properties are sensitive to the presence of specific analytes.